Semiconductor sensor and manufacturing method of sensor body for semiconductor sensor

ABSTRACT

A semiconductor sensor of which the thickness may be reduced and a method of manufacturing a sensor body for the semiconductor sensor are provided. A total length L 1  of a weight portion  5  and an additional weight portion  3  as measured in an extending direction of a centerline C is determined to be shorter than a length L 2  of a support portion  7  as measured in the extending direction of the centerline C. The weight portion  5  and the additional weight portion  3  are received within a space  15  defined, being surrounded by the support portion  7 . Then, dimensions and shapes of the weight portion  5  and the additional weight portion  3  are determined to allow the weight portion  5  and the additional weight portion  3  to move within the space  15.

TECHNICAL FIELD

The present invention relates to a semiconductor sensor and a method ofmanufacturing a sensor body for the semiconductor sensor. Morespecifically, the present invention relates to a semiconductor sensorcapable of measuring acceleration in a predetermined direction caused byforce externally applied, and gravitational acceleration in apredetermined direction in a stationary state, which is applied byinclining the semiconductor sensor, or a semiconductor sensor used as agyroscope, and a manufacturing method of a sensor body used for thesemiconductor sensor.

BACKGROUND ART

Japanese Patent Application Publication No. 2004-125704 (PatentDocument 1) discloses an example of semiconductor sensor including asensor body, an additional weight portion, and a pedestal. The sensorbody includes a weight portion disposed in a central portion thereof, acylindrical support portion disposed in an outer peripheral portionthereof, and a diaphragm portion disposed between the weight portion andthe support portion. Then, the support portion is supported by thecylindrical pedestal. The additional weight portion is fixed to an endof the weight portion and is arranged in a space surrounded by thepedestal and the support portion. In a semiconductor acceleration sensorof this type, based on acceleration caused by force externally appliedor gravitational acceleration applied in a state where the sensor isinclined, the weight portion and the additional weight portion aremoved, and the diaphragm portion is thereby distorted. Then, each sensorelement formed on the diaphragm portion accordingly outputs a detectionsignal indicative of acceleration corresponding to the amount ofdistortion.

Patent Document 1: Japanese Patent Application Publication No.2004-125704 DISCLOSURE OF THE INVENTION Problem to be Solved by theInvention

In the conventional semiconductor sensor, however, the support portionis supported by the cylindrical pedestal. Accordingly, there is a limitto reducing the thickness of the semiconductor sensor including the sizeof the pedestal.

An object of the present invention is to provide a semiconductor sensorof which the thickness may be reduced, and a method of manufacturing asensor body for the semiconductor sensor.

Another object of the present invention is to provide a semiconductorsensor which does not need a pedestal that supports a support portionand a method of manufacturing the semiconductor sensor.

Means for Solving the Problem

A semiconductor sensor, improvement of which is aimed at by the presentinvention comprises: a sensor body including a weight portion disposedin a central portion thereof, a cylindrical support portion disposed inan outer peripheral portion thereof, and a diaphragm portion disposedbetween the weight portion and the support portion; and an additionalweight portion fixed to the weight portion so that a centerline passingthrough the center of the weight portion and extending in a directionorthogonal to an extending direction of the diaphragm portion passesthrough the center of gravity of the additional weight portion. In thepresent invention, the total length of the weight portion and theadditional weight portion as measured in an extending direction of thecenterline is shorter than the length of the support portion as measuredin the extending direction of the centerline. Then, the weight portionand the additional weight portion have dimensions and shapes that allowmovement thereof within a shape which is defined, being surrounded bythe support portion. When the total length of the weight portion and theadditional weight portion as measured in the extending direction of thecenterline is defined to be shorter than the length of the supportportion as measured in the extending direction of the centerline as inthe present invention, the weight portion and the additional weightportion may be received within the space surrounded by the supportportion. For this reason, it is not necessary to provide a pedestal thatsupports the support portion as in the conventional art, because theweight portion and the additional weight portion individually have thedimensions and shape that allow movement thereof within the spacesurrounded by the support portion. The number of components of thesemiconductor sensor may be thereby reduced, so that the thickness ofthe semiconductor sensor may be reduced.

The additional weight portion may be structured to have an upper surfacethat faces a back surface of the diaphragm portion, a lower surface thatopposes the upper surface in the extending direction of the centerline,and an outer peripheral surface located between the upper and lowersurfaces. The outer peripheral surface faces the support portion. Here,preferably, a shape of an inner peripheral surface of the supportportion that faces the additional weight portion and a shape of theadditional weight portion are determined so that, when the additionalweight portion is displaced toward the diaphragm portion by apredetermined amount, an outside corner portion formed between the outerperipheral surface and the upper surface of the additional weightportion comes to abut against the inner peripheral surface of thesupport portion, thereby limiting an amount of the displacement of theadditional weight portion toward the diaphragm portion. With thisarrangement, when acceleration is applied to the semiconductor sensorand then the additional weight portion is going to move more thannecessary, the outside corner portion comes to abut against the innerperipheral surface of the support portion. The displacement amount ofthe additional weight portion is thereby limited within a predeterminedrange. For this reason, the diaphragm portion may be prevented frombeing broken or damaged due to the movement of the additional weightportion.

Another semiconductor sensor of the present invention comprises: asensor body including a weight portion disposed in a central portionthereof, a cylindrical support portion disposed in an outer peripheralportion thereof, and a diaphragm portion disposed between the weightportion and the support portion. Then, the length of the weight portionas measured in an extending direction of a centerline is shorter thanthe length of the support portion as measured in the extending directionof the centerline. The weight portion has dimensions and a shape thatallow movement thereof within a space surrounded by the support portion.In the semiconductor sensor of this type as well, it is not necessary toprovide a pedestal that supports the support portion as in theconventional art. The number of components of the semiconductor sensormay be thereby reduced, so that the thickness of the semiconductorsensor may be reduced.

The sensor body used for a semiconductor sensor of the present inventionmay be manufactured as follows. First, an insulating layer is formed onone of the surfaces of the semiconductor substrate. The insulating layeris coated with a photosensitive resist, thereby forming a firstunphotosensitized resist layer. Next, ultraviolet light is irradiatedonto the first unphotosensitized resist layer through a photomask andthen the irradiated first unphotosensitized resist layer is developed,thereby forming on the one surface of the semiconductor substrate afirst resist layer having a first etching opening of a predeterminedshape. The first resist layer covers a portion where the support portionis to be formed. Then, the insulating layer is etched through the firstetching opening to remove the insulating layer located in a portioncorresponding to the first etching opening, thereby forming a secondetching opening in the insulating layer.

Next, the first resist layer is removed, and then anisotropic etching isapplied to the semiconductor substrate through the second etchingopening, thereby forming a concave portion in the semiconductorsubstrate.

Next, a wall surface insulating film is formed on an inner wall surfaceof the concave portion. Then, the wall surface insulating film and theinsulating layer continuous with the wall surface insulating film arecoated with a photosensitive resist, thereby forming a secondunphotosensitized resist layer. Ultraviolet light is irradiated onto thesecond unphotosensitized resist layer through a photomask and then theirradiated second unphotosensitized resist layer is developed, therebyforming a second resist layer of a predetermined shape and a thirdresist layer. The second resist layer is located on a central locationof the concave portion. The second resist layer has an area smaller thanan area of a bottom surface of the concave portion and covers a portionwhere the weight portion is to be formed. The third resist layer coversthe portion surrounding the concave portion where the support portion isto be formed. The second and third resist layers define a third etchingopening therebetween.

Next, the wall surface insulating film is etched through the thirdetching opening, thereby forming a fourth annular etching opening in thewall surface insulating film. Then, after removing the second and thirdresist layers, anisotropic etching is applied to the semiconductorsubstrate through the fourth etching opening, thereby forming an annularconcave portion in a portion of the semiconductor substrate located on abottom of the concave portion. Then, the diaphragm portion is defined bya portion of the semiconductor substrate that corresponds to a bottomsurface of the annular concave portion, and the weight portion isdefined by the portion of the semiconductor substrate that is left on acentral location of the annular concave portion.

With this arrangement, such sensor body may readily be formed so as tohave the length of the weight portion in the extending direction of thecenterline which is shorter than the length of the support portion inthe extending direction of the centerline.

Wet etching or dry etching may be employed.

The insulating layer may be of a two-layered structure, comprising asilicon oxide film formed by thermally oxidizing the surface of thesemiconductor substrate and a silicon nitride film formed on the siliconoxide film by thin-film formation technique, for example. With thisarrangement, adhesion of the silicon nitride film to the semiconductorsubstrate is improved.

The wall surface insulating film may be formed of a silicon nitride filmformed by thin-film formation technique.

The process of irradiating ultraviolet light onto the secondunphotosensitized resist layer through the photomask may comprise twosteps, a first irradiation step and a second irradiation step. In thefirst irradiation step, the ultraviolet light is irradiated onto thesecond unphotosensitized resist layer through a first negativephotomask, thereby cross-linking a portion of the secondunphotosensitized resist layer where the support portion is to beformed. In the second irradiation step, the ultraviolet light isirradiated onto the second unphotosensitized resist layer through asecond negative photomask after or before the first irradiation step,thereby cross-linking a portion of the second unphotosensitized resistlayer where the weight portion is to be formed. With this arrangement,the second and third resist layers of accurate shapes and dimensions maybe formed.

The first negative photomask may comprise: a main portion through whichthe ultraviolet light passes, and a mask portion formed on a centrallocation of an opposing surface of the main portion that faces thesecond unphotosensitized resist layer. The mask portion may be so formedthat the ultraviolet light is not irradiated onto a portion of thesecond unphotosensitized resist layer other than a portion of the secondunphotosensitized resist layer where the support portion is to beformed.

The second negative photomask may comprise a main portion, a first maskportion, and a second mask portion.

The main portion includes a base portion that faces the secondunphotosensitized resist layer, and a projecting portion having a shapethat projects from the base portion along an inner wall surface of theconcave portion. The ultraviolet light passes through the main portion.The first mask portion is annularly formed on an irradiation surface ofthe base portion onto which the ultraviolet light is to be irradiated.The second mask portion is annularly formed on a location of an opposingsurface of the projecting portion that faces the secondunphotosensitized resist layer and faces the bottom surface of theconcave portion. The second mask portion is formed so that theultraviolet light that has entered through a portion where the firstmask portion is not formed is not irradiated onto portions of the secondunphotosensitized resist layer other than a portion of the secondunphotosensitized resist layer where the weight portion is to be formed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a semiconductor sensor according to a firstembodiment of the present invention.

FIG. 2 is a sectional view taken along line II-II of FIG. 1.

FIGS. 3A to 3F are used for explaining a method of manufacturing asensor body for the semiconductor sensor shown in FIG. 1.

FIGS. 4A to 4E are used for explaining the method of manufacturing thesensor body for the semiconductor sensor shown in FIG. 1.

FIGS. 5A and 5B are used for explaining in detail steps of formingsecond and third resist layers in the manufacturing method of the sensorbody shown in FIGS. 4A to 4E.

FIG. 6 is used for explaining a further step of forming the second andthird resist layers in the manufacturing method of the sensor body shownin FIG. 4.

FIG. 7 is a sectional view of a semiconductor sensor according to asecond embodiment of the present invention.

FIG. 8 is a sectional view of a semiconductor sensor according to athird embodiment of the present invention.

FIG. 9 is a sectional view of a semiconductor sensor according to afourth embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described in detail withreference to accompanying drawings. FIG. 1 is a plan view of asemiconductor sensor in an embodiment (a first embodiment) of thepresent invention that has been applied to an acceleration sensor. FIG.2 is a sectional view taken along line II-II of FIG. 1. As shown in thefigures, the semiconductor sensor in this embodiment includes a sensorbody 1 and an additional weight portion 3 fixed onto the sensor body 1.

The sensor body 1 is formed by applying anisotropic etching to asemiconductor crystal substrate formed of single-crystal silicon so thata weight portion 5 is disposed in a central portion of the sensor body1, a cylindrical support portion 7 is disposed in an outer peripheralportion of the sensor body 1, and a diaphragm portion 9 havingflexibility is defined between the weight portion 5 and the supportportion 7. On at least one of the diaphragm portion 9 and the supportportion 7 on a surface of the sensor body 1, a plurality of sensorelements not shown are formed. The sensor elements are formed ofdiffused resistors for acceleration detection. A plurality of electrodes11 are formed on the support portion 7. In the semiconductor sensor inthis embodiment, the weight portion 5 and the additional weight portion3 are moved by force based on acceleration caused by force appliedexternally or gravitational acceleration applied in an inclinedstationary state of the semiconductor sensor. The diaphragm portion 9 isthereby flexed. Resistance values of the respective diffused resistorsconstituting the sensor elements are changed, thereby detecting theacceleration in three axial directions corresponding to an amount ofdistortion.

The weight portion 5 is shaped to project from the diaphragm portion 9.The direction where the weight portion 5 projects is opposite to adirection toward a surface of the support portion 7 on which electrodes11 are provided (or a direction toward the back surface of the diaphragmportion 9). The weight portion 5 has a cross sectional surface of apolygon. A virtual line that passes through the center of the weightportion 5 and extends in a direction orthogonal to a direction in whichthe diaphragm portion 9 extends is indicated by a virtual centerline C.An outer peripheral surface 5 a of the weight portion 5 centering on thecenterline C is inclined so that the further the outer peripheralsurface 5 a is away from the diaphragm portion 9, the closer the outerperipheral surface 5 a is to the centerline C. Then, the total length L1of the weight portion 5 and the additional weight portion 3 as measuredin an extending direction of the centerline C is shorter than the lengthL2 of the support portion 7 as measured in the extending direction ofthe centerline C, which will be described later.

The support portion 7 has a rectangular annular shape. An innerperipheral surface 13 of the support portion 7 that faces the additionalweight portion 3 is structured by an annular arrangement of fourtrapezoidal inclined surfaces of substantially the same shape so as tofollow the outer peripheral surface of a frust-pyramidal or truncatedpyramid space defined by the support portion 7. The inner peripheralsurface 13 is so inclined that the further the inner peripheral surface13 is away from the diaphragm portion 9, the further the innerperipheral surface 13 is apart from the centerline C. In thisembodiment, an inclination angle θ1 of the inner peripheral surface 13with respect to the centerline C is 36 degrees. With such a structure ofthe inner peripheral surface 13 of the support portion 7, a space 15containing the weight portion 5, surrounded by the support portion 7 hasa frust-pyramidal or truncated pyramid shape of which the crosssectional area is reduced more toward the diaphragm portion 9.

The additional weight portion 3 is shaped like a circular plate, and isformed of tungsten. This additional weight portion 3 includes an uppersurface 3 a shaped like a circular plate, which extends along thediaphragm portion 9 and faces the back surface of the diaphragm portion9, a lower surface 3 b that opposes the upper surface 3 a in theextending direction of the centerline C, and an outer peripheral surface3 c located between the upper surface 3 a and the lower surface 3 b. Theouter peripheral surface 3 c faces the support portion 7. For thisreason, an outside corner portion 3 d is formed between the outerperipheral surface 3 c and the upper surface 3 a. The outside cornerportion 3 d has a crossing angle of 90 degrees between the outerperipheral surface 3 c and the upper surface 3 a. Then, the centralportion of the upper surface 3 a is fixed to the bottom of the weightportion 5 using an adhesive. This additional weight portion 3 is fixedonto the weight portion 5 so that the centerline C of the weight portion5 passes through the center of gravity of the additional weight portion3. The weight portion 5 and the additional weight portion 3 are receivedin the space 15 surrounded by the support portion 7. Then, the weightportion 5 and the additional weight portion 3 have dimensions and shapesthat allow movement thereof within the space 15. In this embodiment,when the additional weight portion 3 is going to move more thannecessary, the outside corner portion 3 d comes to abut against theinner peripheral surface 13 of the support portion 7. A displacementamount of the additional weight portion 3 is thereby limited within apredetermined range.

A manufacturing method of the sensor body 1 used in the semiconductorsensor in this embodiment will be described with reference to FIGS. 3Ato 3F and FIGS. 4A to 4E.

First, as shown in FIG. 3A, an insulating layer 23 is formed each onboth surfaces of the semiconductor substrate 21. The insulating layer 23may be formed of a single layer or multiple layers. In this embodiment,the insulating layer 23 is of a two-layered structure, comprising asilicon oxide film (SiO₂ film) 23A formed by thermally oxidizing thesurface of the semiconductor substrate 21 and a silicon nitride film(Si₃N₄ film) 23B formed on the silicon oxide film 23A by thin-filmformation technique.

Next, as shown in FIG. 3B, a first unphotosensitized resist layer 25 isformed by coating the insulating layer 23 with a photosensitive resist.Then, as shown in FIG. 3C, a first resist layer 29 having a firstetching opening 27 of a predetermined shape is formed on one surface ofthe semiconductor substrate 21 (which is the lower surface in the pageof FIG. 3C) after ultraviolet light has been irradiated onto the firstunphotosensitized resist layer 25 through a first photomask and then theirradiated first unphotosensitized layer has been developed. The firstresist layer 29 covers a portion where the support portion 7 is to beformed in a subsequent step. Next, as shown in FIG. 3D, the insulatinglayer is etched through the first etching opening 27, using a wetetching solution, to remove a portion of the insulating layer 23 thatcorresponds to the first etching opening 27. A second etching opening 31is thereby formed in the insulating layer 23. In this embodiment, forthe silicon nitride film (Si₃N₄ film) 23B, phosphoric acid is used as awet etching solution. Then, for the silicon oxide film (SiO₂ film) 23A,an aqueous solution of buffered hydrofluoric acid is employed as a wetetching solution. Then, the first resist layer 29 is removed.

Next, as shown in FIG. 3E, anisotropic etching is applied to thesemiconductor substrate through the second etching opening 31, using ananisotropic etching solution. A concave portion 21 a is thereby formedin the semiconductor substrate 21. In this embodiment, an aqueoussolution of KOH is employed as an anisotropic etching solution. Next, asshown in FIG. 3F, a wall surface insulating film 33 is formed on aninner peripheral surface 21 b of the concave portion 21 a. In thisembodiment, the wall surface insulating film 33 is formed of the siliconnitride film (Si₃N₄ film) formed by thin-film formation technique.

Next, as shown in FIG. 4A, the wall surface insulating film 33 and theinsulating layer 23 that is continuous with the wall surface insulatingfilm 33 are coated with a photosensitive resist, thereby forming asecond unphotosensitized resist layer 35. In this embodiment, theunphotosensitized resist layers 35 are formed each on the entire upperand lower surfaces of the semiconductor substrate 21. Next, as shown inFIG. 4B, ultraviolet light is irradiated onto the secondunphotosensitized resist layer 35, thereby forming a second resist layer37 of a predetermined shape and a third resist layer 39. The secondresist layer 37 is disposed on a central location of the concave portion21 a. The second resist layer 37 has an area smaller than an area of abottom surface of the concave portion 21 a. The third resist layer 39covers the insulating layer 23 around the concave portion 21 a. Thesecond resist layer 37 covers a portion where the weight portion 5 is tobe formed in a subsequent step, while the third resist layer 39 coversthe portion where the support portion 7 is to be formed. The second andthird resist layers define a third etching opening 41 therebetween.

In this embodiment, the ultraviolet light is irradiated in the followingmanner. First, a first negative photomask R1 is prepared, as shown inFIG. 5A. The first negative photomask R1 has a main portion R11 and amask portion M1. The main portion R11 is formed of glass, through whichthe ultraviolet light passes. The mask portion M1 is formed on a centralportion of an opposing surface R12 of the main portion R11. The opposingsurface R12 faces the second unphotosensitized resist layer 35. The maskportion M1 is shaped so that ultraviolet light UV which has entered themain body portion R11 is masked and is not irradiated onto portions ofthe second unphotosensitized resist layer 35 other than a portion of thesecond unphotosensitized resist layer 35 around the concave portion 21 a(portion where the support portion 7 is to be formed in a subsequentstep). Then, the ultraviolet light UV is irradiated onto the secondunphotosensitized resist layer 35 through the first negative photomaskR1. With this arrangement, the portion of the second unphotosensitizedresist layer 35 where the support portion 7 is to be formed iscross-linked (in a first irradiation step).

Next, as shown in FIG. 5B, a second negative photomask R2 is prepared.The second negative photomask R2 also has a main portion R21 formed ofglass, through which the ultraviolet light passes. The main portion R21has a base portion R22 that faces the second unphotosensitized resistlayer 35, and a projecting portion R23 shaped to project from the baseportion R22 along the inner wall surface of the concave portion 21 a. Afirst annular mask portion M2 is formed on an irradiation surface R24 ofthe base portion R22 onto which the ultraviolet light is to beirradiated. A second annular mask portion M3 is formed on an opposingsurface R25 of the projecting portion R23 that faces the secondunphotosensitized resist layer 35. The second annular mask portion M3 isshaped so that the ultraviolet light UV which has entered through aportion where the first mask portion M2 is not provided is masked and isnot irradiated onto portions of the second unphotosensitized resistlayer 35 other than a portion of the second unphotosensitized resistlayer 35 where the weight portion 5 is to be formed. Then, theultraviolet light UV is irradiated onto the second unphotosensitizedresist layer 35 through the second negative photomask R2. With thisarrangement, the weight portion 5 of the second unphotosensitized resistlayer 35 is cross-linked (in a second irradiation step).

Next, using a developing solution, a portion of the secondunphotosensitized resist layer 35 between a central portion of theconcave portion 21 a and a peripheral portion of the concave portion 21a (portion onto which the ultraviolet light UV is not irradiated andwhich is not therefore cross-linked) is removed. In the embodimentdescribed above, after cross-linking the portion of the secondunphotosensitized resist layer 35 where the support portion is to beformed, the portion where the weight portion 5 to be formed iscross-linked. The order in which the first irradiation step and thesecond irradiation step are performed may be reversed. Aftercross-linking the portion of the second unphotosensitized resist layer35 where the weight portion 5 is to be formed, the portion where thesupport portion 7 is to be formed may be cross-linked.

When a material that decomposes by ultraviolet light is employed for thesecond unphotosensitized resist layer 35, a positive photomask should beemployed.

The ultraviolet light may also be irradiated, using a negative photomaskR3 as shown in FIG. 6. On the negative photomask R3, mask portions M4are formed so that the ultraviolet light is not irradiated onto theportions of the second unphotosensitized resist layer 35 other thanportions of the second unphotosensitized resist layer corresponding tothe central and surrounding portions of the concave portion 21 a.

Next, as shown in FIG. 4C, the wall surface insulating film is etchedthrough the third etching opening 41, using a wet etching solution. Afourth annular etching opening 43 is thereby formed in the wall surfaceinsulating film 33. Then, the second resist layer 37 and the thirdresist layer 39 are removed.

Next, as shown in FIG. 4D, anisotropic etching is applied to thesemiconductor substrate through the fourth etching opening 43, using ananisotropic etching solution, thereby forming an annular concave portion45 in a portion of the semiconductor substrate 21 located on a bottom ofthe concave portion 21 a. Then, as shown in FIG. 4E, the wall surfaceinsulating film 33 and the insulating layer 23 on a bottom of thesupport portion 7 are removed. Then, the diaphragm portion 9 is definedby a portion of the semiconductor substrate 21 that corresponds to abottom surface of the annular concave portion 45, and the weight portion5 is defined by a portion of the semiconductor substrate 21 that is lefton a central location of the annular concave portion 45, therebycompleting the formation of the sensor body for a semiconductor sensor.

According to the semiconductor sensor in this embodiment, the totallength L1 of the weight portion 5 and the additional weight portion 3 asmeasured in the extending direction of the centerline C is shorter thanthe length L2 of the support portion 7 as measured in the extendingdirection of the centerline C. Accordingly, the weight portion 5 and theadditional weight portion 3 may be received within the space 15surrounded by the support portion 7. For this reason, the weight portion5 and the additional weight portion 3 have the dimensions and shapesthat allow movement thereof within the space 15. Thus, it is notnecessary to provide a pedestal that supports the support portion as inthe conventional art. The number of components of the semiconductorsensor may be thereby reduced, so that the thickness of thesemiconductor sensor may be reduced.

FIG. 7 is a sectional view of a semiconductor sensor in a secondembodiment of the present invention. In this embodiment, referencenumerals obtained by adding 100 to reference numerals used in the firstembodiment are employed for components corresponding to those in thefirst embodiment, respectively. The semiconductor sensor in thisembodiment is structured by a sensor body 101 alone. The sensor body 101includes a weight portion 105 disposed in a central portion thereof, acylindrical support portion 107 disposed in an outer peripheral portionthereof, and a diaphragm portion 109 disposed between the weight portion105 and the support portion 107. The length of the weight portion 105 asmeasured in an extending direction of the centerline C is shorter thanthe length of the support portion 107 as measured in the extendingdirection of the centerline C. Then, the weight portion 105 hasdimensions and a shape that allow movement thereof within a space 115surrounded by the support portion 107.

An outer peripheral surface 105 a of the weight portion 105, centeringon the centerline C, extends in parallel with the centerline C.

An inner peripheral surface 113A of the support portion 107 in a regionA1 that faces the weight portion 105 extends in parallel with thecenterline C. An inner peripheral surface 113B of the support portion107 in a region A2 that does not face the weight portion 105 is inclinedso that the further the inner peripheral surface 113B is away from thediaphragm portion 109, the further the inner peripheral surface 113B isapart from the centerline C.

In the semiconductor sensor in this embodiment, dry etching is employedfor etching applied to the region A1, wet etching for etching applied tothe region A2. FIG. 8 is a sectional view of a semiconductor sensor in athird embodiment of the present invention. In this embodiment, referencenumerals obtained by adding 200 to the reference numerals used in thefirst embodiment are employed for components corresponding to those inthe first embodiment, respectively. The semiconductor sensor in thisembodiment is also structured by a sensor body 201 alone. In thesemiconductor sensor in this embodiment, an outer peripheral surface 205a of a weight portion 205, centering on the centerline C, is inclined sothat the further the outer peripheral surface 205 a is away from adiaphragm portion 209, the closer the outer peripheral surface 205 a isto the centerline C.

An inner peripheral surface 213A of a support portion 207 in the regionA1 that faces the weight portion 205 is inclined so that the further theinner peripheral surface 213A is away from the diaphragm portion 209,the further inner peripheral surface 213A is apart from the centerlineC. An inner peripheral surface 213B of the support portion 207 in aregion A2 that does not face the weight portion 205 extends in parallelwith the centerline C.

In the semiconductor sensor in this embodiment, wet etching is employedfor etching applied to the region A1, and dry etching for etchingapplied to the region A2.

FIG. 9 is a sectional view of a semiconductor sensor in a fourthembodiment of the present invention. In this embodiment, referencenumerals obtained by adding 300 to the reference numerals used in thefirst embodiment are employed for components corresponding to those inthe first embodiment, respectively. The semiconductor sensor in thisembodiment is also structured by a sensor body 301 alone. In thesemiconductor sensor in this embodiment, an outer peripheral surface 305a of a weight portion 305, centering on the centerline C, is inclined sothat the further the outer peripheral surface 305 a is away from adiaphragm portion 309, the closer the outer peripheral surface 305 a isto the centerline C.

An inner peripheral surface 313A of a support portion 307 in the regionA1 that faces the weight portion 305 is inclined so that the further theinner peripheral surface 313A is away from the diaphragm portion 309,the further the inner peripheral surface 313A is apart from thecenterline C. An inner peripheral surface 313B of the support portion307 in the region A2 that does not face the weight portion 305 iscontinuous with the inner peripheral surface 313A, and is also inclinedso that the further the inner peripheral surface 313B is away from thediaphragm portion 309, the further the inner peripheral surface 313B isapart from the centerline C.

In the semiconductor sensor in this embodiment, wet etching is employedfor etching applied to the regions A1 and A2.

1. A semiconductor sensor comprising: a sensor body including a weightportion disposed in a central portion thereof, a cylindrical supportportion disposed in an outer peripheral portion thereof, and a diaphragmportion disposed between the weight portion and the support portion; andan additional weight portion fixed onto the weight portion so that acenterline passing through the center of the weight portion andextending in a direction orthogonal to an extending direction of thediaphragm portion passes through the center of gravity of the additionalweight portion; wherein a total length of the weight portion and theadditional weight portion as measured in an extending direction of thecenterline is shorter than a length of the support portion as measuredin the extending direction of the centerline; the weight portion and theadditional weight portion are received within a space surrounded by thesupport portion; and dimensions and shapes of the weight portion and theadditional weight portion are determined to allow the weight portion andthe additional weight portion to move within the space.
 2. Thesemiconductor sensor according to claim 1, wherein the additional weightportion includes an upper surface that faces a back surface of thediaphragm portion, a lower surface that opposes the upper surface in theextending direction of the centerline, and an outer peripheral surfacelocated between the upper and lower surfaces, facing the supportportion; and a shape of an inner peripheral surface of the supportportion that faces the additional weight portion and a shape of theadditional weight portion are determined so that, when the additionalweight portion is displaced toward the diaphragm portion by apredetermined amount, an outside corner portion formed between the outerperipheral surface and the upper surface of the additional weightportion comes to abut against the inner peripheral surface of thesupport portion, thereby limiting an amount of the displacement of theadditional weight portion toward the diaphragm portion.
 3. Asemiconductor sensor comprising: a sensor body including a weightportion disposed in a central portion thereof, a cylindrical supportportion disposed in an outer peripheral portion thereof, and a diaphragmportion disposed between the weight portion and the support portion,wherein a length of the weight portion as measured in an extendingdirection of a centerline is shorter than a length of the supportportion as measured in the extending direction of the centerline; anddimensions and a shape of the weight portion are determined to allow theweight portion to move within a space surrounded by the support portion.4. A method of manufacturing a sensor body for a semiconductor sensor byetching a semiconductor substrate, the sensor body including a weightportion disposed in a central portion thereof, a cylindrical supportportion disposed in an outer peripheral portion thereof, and a diaphragmportion disposed between the weight portion and the support portion, themethod comprising: forming an insulating layer on one surface of thesemiconductor substrate; coating the insulating layer with aphotosensitive resist, thereby forming a first unphotosensitized resistlayer; irradiating ultraviolet light onto the first unphotosensitizedresist layer through a photomask and then developing the irradiatedfirst unphotosensitized resist layer, thereby forming on the one surfaceof the semiconductor substrate a first resist layer having a firstetching opening of a predetermined shape, the first resist layercovering a portion where the support portion is to be formed; etchingthe insulating layer through the first etching opening to remove aportion of the insulating layer that corresponds to the first etchingopening, thereby forming a second etching opening in the insulatinglayer; removing the first resist layer and then applying anisotropicetching to the semiconductor substrate through the second etchingopening, thereby forming a concave portion in the semiconductorsubstrate; forming a wall surface insulating film on an inner wallsurface of the concave portion; coating the wall surface insulating filmand the insulating layer continuous with the wall surface insulatingfilm with a photosensitive resist, thereby forming a secondunphotosensitized resist layer; irradiating ultraviolet light onto thesecond unphotosensitized resist layer through a photomask and thendeveloping the irradiated second unphotosensitized resist layer, therebyforming a second resist layer of a predetermined shape and a thirdresist layer, the second resist layer being disposed on a centrallocation of the concave portion, having a smaller area than an area of abottom surface of the concave portion, and covering a portion where theweight portion is to be formed, the third resist layer covering aportion located around the concave portion, where the support portion isto be formed, the second and third resist layers defining a thirdetching opening therebetween; etching the wall surface insulating filmthrough the third etching opening, thereby forming a fourth annularetching opening in the wall surface insulating film; and removing thesecond and third resist layers and then applying anisotropic etching tothe semiconductor substrate through the fourth etching opening, therebyforming an annular concave portion in a portion of the semiconductorsubstrate located on a bottom of the concave portion, wherein thediaphragm portion is defined by a portion of the semiconductor substratecorresponding to a bottom surface of the annular concave portion, andthe weight portion is defined by the portion of the semiconductorsubstrate that is left on a central location of the annular concaveportion.
 5. The method of manufacturing a sensor body for asemiconductor sensor according to claim 4, wherein the insulating layeris of a two-layered structure comprising a silicon oxide film formed bythermally oxidizing the one surface of the semiconductor substrate and asilicon nitride film formed on the silicon oxide film by thin-filmformation technique.
 6. The method of manufacturing a sensor body for asemiconductor sensor according to claim 4, wherein the wall surfaceinsulating film is formed of a silicon nitride film formed by thin-filmformation technique.
 7. The method of manufacturing a sensor body for asemiconductor sensor according to claim 4, wherein irradiation of theultraviolet light performed onto the second unphotosensitized resistlayer through the photomask comprises: a first irradiation step ofirradiating the ultraviolet light onto the second unphotosensitizedresist layer through a first negative photomask, thereby cross-linking aportion of the second unphotosensitized resist layer where the supportportion is to be formed; and a second irradiation step of irradiatingthe ultraviolet light onto the second unphotosensitized resist layerthrough a second negative photomask after or before the firstirradiation step, thereby cross-linking a portion of the secondunphotosensitized resist layer where the weight portion is to be formed.8. The method of manufacturing a sensor body for a semiconductor sensoraccording to claim 4, wherein the first negative photomask comprises: amain portion through which the ultraviolet light passes; and a maskportion that is formed on a central location of an opposing surface ofthe main portion that faces the second unphotosensitized resist layer sothat the ultraviolet light is not irradiated onto portions of the secondunphotosensitized resist layer other than a portion of the secondunphotosensitized resist layer where the support portion is to beformed; and the second negative photomask comprises: a main portionincluding a base portion that faces the second unphotosensitized resistlayer, and a projecting portion shaped to project from the base portionalong an inner wall surface of the concave portion, the ultravioletlight passing through the main portion; a first mask portion annularlyformed on an irradiation surface of the base portion onto which theultraviolet light is to be irradiated; and a second mask portionannularly formed on a portion of an opposing surface of the projectingportion that faces the second unphotosensitized layer and faces thebottom surface of the concave portion, so that the ultraviolet lightthat has entered through a portion where the first mask portion is notformed is not irradiated onto portions of the second unphotosensitizedportion other than a portion of the second unphotosensitized resistlayer where the weight portion is to be formed.
 9. The sensor body for asemiconductor sensor manufactured by the manufacturing method accordingto claim 4.